Solvent for rayon and rayon treating solution



Patented Jan. 13, 194

SOLVENT FOR RAYON AND RAYON TREATING SOLUTION Charles L. Mantell, Manhasset, N. Y., assignor to United Merchants & Manufacturers, Inc., Wilmington, Del., a corporation of Delaware No Drawing. Application September 19, 1945, Serial No. 617,449

11 Claims. (Cl. 106-203) This invention relates to a solvent for rayon, sometimes referred to as artificial silk or regenerated cellulose.

A primary object of the invention is to provide a solvent useful over a relatively wide temperature range, by means of which rayon, either new or in the form of all kinds of factory or mill wastes, can be reduced to a state suitable for further use. Another object is to provide a method of salvaging cloth which has been finished for a particular purpose, say with a rayon coating incorporating an inert dye, but which can no longer be used as intended, and which would represent a loss unless the finish could be removed. A further object is to provide a cheap and readily obtainable solution of rayon adapted to be used as a cloth finishing composition. other objects and advantages will appear hereinafter.

It has heretofore been proposed to dissolve rayon in an aqueous solution of sodium zincate. There are, however, several disadvantages inherent in such use of sodium zincate, among which are the low treating temperatures required, i. e., not above 5C. and preferably below, involving the use of expensive refrigeration equipment and material. Following such treatment, the cellulose solution must then be aged for a considerable period before it is ready for use, entailing a loss of time. Furthermore, sodium zincate solutions have a restricted field of application, exhibiting solvency power for but a lim- .ited number of materials and being inefiective as to others. In addition, these solutions tend to be unusually viscous, and this condition becomes excessively pronounced as the cellulosic concentration is increased, thus causing handling disadvantages. Attempts have been made to overcome the disadvantage of the low temperature requirements of the foregoing process but by the use of such excessive amounts of sodium zincate as to introduce other difiiculties.

According to the present invention, it has been found that the solvency power of sodium zincate solutions is improved by the addition of urea, the improvement being particularly notable with respect to the increased number and variety of forms of rayon which may be treated, i. e., mill and factory wastes, and also with respect to the operable temperature range. In the latter respect it is to be noted that while the solvent can be used at low temperatures, it is especially advantageous in that it is highly effective at room temperature and up to about 120 F.

The solvent may be prepared by mixing to- 2 gether an alkaline aqueous solution of sodium zincate and urea, or by adding urea and zinc oxide to an aqueous solution of sodium hydroxide, sodium zincate being formed by reaction of the latter two substances. Besides the sodium compounds, compounds of other alkali metals may be used, such as potassium zincate, or potassium hydroxide, although sodium compounds are preferred. It is to be understood that in referring to the zinc oxide content of the solution it is intended to include the oxide added as such or as comprised in the alkali metal zincate added to the solution or formed therein. The amount of urea may be varied from about 4 to about 10% by weight, preferably from about 6 to 10%, At concentrations below this range, the solvency power of the solvent is decreased, while at concentrations above 10%, no worth-while improvement results. Zinc oxide, whether added as such or in the form of the zincate, may be present in amounts ranging from 2% by weight to the saturation percentage, calculated as zinc oxide; While the caustic may be varied from about 7 to about 15% by weight. As in the case of urea, solvency power is afiected by going below the minimum concentrations of the zinc oxide and caustic; above the maximum concentrations given, there is no worthwhile improvement in results. A particularly good solvent is one composed of 4.5% zinc oxide, 10% caustic, 10% urea, and the remainder water.

Compounds which, when added to a caustic zincate solution, hydrolyze to form urea, may be used in making up the solvent. Such compounds may include, for example, cyanamide, guanidine, guanylurea, etc. In the premises, it will be understood that the term "urea as used herein is intended to include urea per se and also compounds which produce urea as in the foregoing manner.

Any type of fabric composed of rayon may be dissolved in the solvent of this invention. Regenerated cellulose fabrics include, for example, yarns, threads, cloth, clippings, card waste, comber wastes, lacings, strings, tire cord, or other waste of rayon made by the viscose, Bemberg, or any other processes.

As already mentioned, the solvent is highly effective at room temperatures and thus eliminates the necessity for refrigeration material or equipment. After thecellulosic materials have been dissolved, the solutions so obtained are ready for use. No aging or ripening to reduce the viscosity is required, as the solutions exhibit good viscosity characteristics at various concentrations of solute.

4 used. Following is an example of applying a finish to a textile fabric:

Example 2 Three grams of regenerated cellulose pulp were Table I .,dissolved inrlll0.cc. of,-an.aqueoussolution containing fl.8 sodium-aineate, 4 4% free sodium Viscosity in poises hydroxide, and 8% urea. A sample of cloth, in Concentration ofcellulosic material, this case marquisette, was immersed in the solupercentbywt- Present Sodium 10 tion, passed through a 6% sulfuric acid settin 8mm Zmmie bath, rinsedand dried. The cloth showed a pick- Ve mu V r y up or-increase in weight of 104%. {f Therayonsolutions described above may, if de- .6 'l gi .sired bedilutedmith water to form less concentrated solutions. -I n some cases it may be desir- The effect of urea upon solvent power, as deter mined by viscosity and clarity tests, is further demonstrated in the following example:

Example 1 h solutionpontaining 12 gms. of caustic soda "Five-gram samples of semi-coarse rayon gwaste were dissolvedin each of these solutions, .and after two hours standing, their viscosities \WGIG measured on a Stormer viscosimeter in which the time of 100 revolutions was noted in -.seconds,.using a EGO- gram loadat room temperature. The viscosity of'a solution to which no urea had been added wasalso taken. Following are the data-obtained:

able to make an initial solution of such concentration-that a gelresults, as by employing high rayon concentrations, say about 6%, and then to form solutitons of lower rapon content as required, by diluting the gel with water. The resultingdiluted solutions may have any rayon concennatio be w tha a wh se a t e p ce- The dilution of the gel may be hastened bypassend-3 grns. ofzinc oxide per 100 cclwasprepared.

-To seven lOO-cc. portionsof this solution there 1 3 along i thelwater hr ushah ie een ..were added amounts of urea ranging from 4 to 10 Y ll asi rthe b en folmd P 2 ting agent wh ch is compat blewith alka li sused th in al formula i t eel. th su s?- quent dilutionof the gel results in solutions of im o d t l t .A examn esp u wettin a e t there ma bg en p ie the alky su f tes a k err l e s. polyal s lene are: .a1 9h9 s and salts of these ,varioiis compounds. The wet-- ting agent may, of course, be employed in fprrnm ti n o te n whi d i s int the gel form.

. An ther ap iw pn o t l e Qns stsJn Grammars-100cessation $553535! th salvaging o clot mad p ma eria othe than rayonand having afinish of rayon. Where no such finish is no longer desirable, it may ,be 70 40 stripped from the cloth by means 9f .the solvent 23 wi h u u s n a a tin th cloth i elf- 15 The following exampleillustratesthis application of the solvent: 34 Example} ovements in the clarity of the solutions were also noted. Thus, a two-inch colm Q a solutipnue iulaced Over a'black teronapaperpatl, the letterbeing inch by inch. This letter was entirely invisible through the solution of caustic zincate containing no urea. It was fairly visible through thesolution contain- .ing 5 gms. of urea, and plainly-visible through the solution containing 10 gms. of-urea.

In pp yi the solvent, rayon as contained in any type of fabric either new or in the form of .waste material, maybe recoveredand reduced to a usable form. -I-f the cellulosic material is permitted to swell a short time in the caustic zincate solution prior to adding the urea, its tendency to become ropey may be avoided and a uniform solution mayrbe rapidly produced. The solution resulting may be used directly as a finishing composition for various ,tentilernaterials. Rayon recovered in this manner from soiled wastes need not .be purified beforeuse but may, ina particular case, be employed without further treatment. Cloth to be finished is .passed through the solution and then the cellulose is reprecipitated on the fibres of the cloth by means .of a coagulent, such as hot or cold water or dilute acid, and the cloth-is rinsed and dried. A 4% solution of cellulo sic material in the solvent has been found suitable and a useful concentration range is 1 to 5%, a h u h high- Q 'l sI. c centra a be Similar .impr

Cotton netting having a finish containing regenerated cellulose and a-pigment was immersed at room temperature in a solvent containing'by weight 4.8% sodium zincate, 4.4% freesodium'hydioxide, 8% urea, v and the remainder water. :When the cloth appeared to be substantially free of the-finish, it was removed, rinsed and soaped clean.

It --will be noted that inert pigments or ;i "lllers forming a part of the finish are also removed in the tripping operation. A variety of finishes can thus be stripped from textile cloths, the conditions-to be observed being that the finish be composed of material substantially soluble in the solvent and that the cloth-be substantially insoluble. In other words, the solvent is selective for regenerated or degraded cellulose but not for cel- 1$ per fi- .st i p ill ma be aide by ,m che r in the c ot t rou the o vent a b u hi 12 lQQ Q 5 h.? dhe i finish- 1' 1? cloth may then be washed with more solvent and finally with water. A counter-flow strippingand washing system, in which the cloth travels in a direction countercurrent to the flow of solvent and wash water, and in which the solvent may be used until it is completely spent, maybe em.- ployed to advantage.

A further advantage .of the solventof this .invention is in connection with the production of de e s on regenera d lee l lose t xt l as in the making of simulated damask. In the latter operation, the cloth is first printed with a resist such as starch or dextrin to protect the printed areas from the action of the solvent, and then the printed cloth is padded through the solvent. After removal of the cloth from the solvent, it may be allowed to stand for a brief period before being neutralized and washed out. The finished cloth shows a clearly discernible design, which is enhanced by dyeing.

In the light of the foregoing description the following is claimed:

1. An aqueous solution for treating rayon made from about '7 to about 15% by weight of alkali metal hydroxide, about 4 to about by weight of urea, and about 2% to the saturation percentage by weighi; of zinc oxide, said saturation percentage of zinc oxide being that amount above which zinc oxide will precipitate from the aqueous solution containing said alkali metal hydroxide, urea, and zinc oxide in the said amounts.

2. Method of removing rayon from textile material containing the same which comprises treating such material with an aqueous solution made from about 7 to about by weight of alkali metal hydroxide, about 4 to about 10% by weight of urea, and about 2% to the saturation percentage by weight of zinc oxide, said saturation percentage of zinc oxide being that amount above which zinc oxide will precipitate from the aqueous solution containing said alkali metal hydroxide, urea, and zinc oxide in the said amounts.

3. Method of stripping a textile material coated with rayon which comprises treating said material with an aqueous solution of about 7 to about 15% by weight of alkali metal hydroxide, about 4 to about 10% by weight of urea, and about 2% to the saturation percentage by weight of zinc oxide, said saturation percentage of zinc oxide being that amount above which zinc oxide will precipitate from the aqueous solution containing said alkali metal hydroxide, urea, and zinc oxide in the said amounts.

4. An aqueous solution for treating rayon consisting essentially of about 10% by weight of caustic soda, about 10% by Weight of urea, and about 4.5% by weight of zinc oxide.

5. Method of removing rayon from textile material containing the same which comprises treating such material with an aqueous solution consisting essentially of about 10% by weight of caustic soda, about 10% by weight of urea, and about 4.5% by weight of zinc oxide.

6. A rayon solution consisting essentially of an aqueous solution having about 10% by weight of caustic soda, about 10% by Weight of urea, about 4.5% by weight of zinc oxide, and about 4% by weight of rayon therein.

7. A rayon solution consisting essentially of an aqueous solution having about 7 to 15% by weight of alkali metal hydroxide, about 2% to the saturation percentage by weight of zinc oxide, about 4 to 10% by weight of urea, and. about 1 to 6% by weight of rayon, said saturation percentage of zinc oxide being that amount above which zinc oxide will precipitate from the aqueou solution containing the said alkali metal hydroxide, urea, and zinc oxide in the said amounts.

8. A rayon solution composition according to claim 10 in which the alkali metal hydroxide is sodium hydroxide.

9. A rayon solution composition according to claim '7 in which the alkali metal hydroxide is sodium hydroxide.

10. A rayon solution consisting essentially of an aqueous solution having about 7 to 15% by weight of alkali metal hydroxide, about 2% to the saturation percentage by weight of zinc oxide, about 4 to 10% by Weight of urea, and incorporating about 1 to 5% by weight of rayon therein, said saturation percentage of zinc oxide being that amount above which zinc oxide will precipitate from the aqueous solution containing said alkali metal hydroxide, urea, and zinc oxide in the said amounts.

11. An aqueous solution according to claim 1 in which the alkali metal hydroxide is sodium hydroxide.

CHARLES L. MAN'IELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

